Why was Kozbi bas Tzur not considered an eshes yefas toar (a non-Jewish woman who is taken captive during wartime and is permitted to her captor) who would then be permitted to Zimri? This question assumes that this was a war situation this is based on the fact that

1) All the nations of Canaan knew that the Jews were coming to conquer them hence Balak sought a preemptive strike (via Bilaam's curse).

2) Sending the women to entice them was a form of (spiritual) attack. Hence they were not offered the same military conditions as the other nations ("just let us pass through").

Does the law of kol haboel aramis (anyone who sleeps with a non-Jewish woman, a zealot can kill him) supersede yefas toar?

I think that Kosbi and Zimri were killed for two main reasons :
1) she convince him to do havoda zara
2) They made love berabim ( even if he brought her in his tent ) meaning every body saw him bringing Kosbi in his tent in order to make love with here

I don't see how this addresses the question posed. Welcome to Mi Yodeya, though; I hope you stick around and post some good questions and answers. You may also wish to register your account, which will give you access to more of the site's features.
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msh210♦Jul 17 '12 at 22:08

@msh210 I think it answers it in the respect that even if this was considered a war and such a situation applies, there are plenty of commentary explaining why Kozbi was in fact NOT permitted to Zimri and thus why she was killed by Pinchas.
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user1292Jul 18 '12 at 0:55